This invention relates to electrical devices such as storage cells, capacitors, and pseudo-capacitors that store electrical energy, and, more particularly, to such devices formed of arrays of fibrous electrodes.
One of the approaches to the storage of electrical energy is a bipolar device in which a voltage is applied across opposing electrodes having an intermediate layer. Electrical charge accumulates on the surfaces of the electrodes. In a temporary storage device such as a capacitor, the charge flows from the electrodes as an electrical current when the applied voltage is removed. In a longer-term storage device such as an electrochemical storage cell, the applied charge causes electrochemical changes in the intermediate layer that converts the electrical energy to chemical energy. The chemical energy can be later released upon the discharge of the electrochemical cell.
The performance of such bipolar electrical storage devices depends in part upon the available surface area of the electrodes. The simplest electrical storage devices use one or more pairs of opposing flat electrodes arranged in a facing relationship. More surface area and thence greater storage capacity and performance can be achieved by making the electrodes in other forms.
Storage devices using rodlike electrodes have been known in the art, see for example, U.S. Pat. No. 4,788,114. In such devices, the rod-shaped electrodes of both types are bundled and connected at opposing ends to an end plate structure. In the case of a storage cell, an electrolyte is introduced between the electrodes. Such storage devices with rodlike electrodes have improved storage capacity as compared with flat-plate bipolar devices.
Although they are operable, the existing electrical storage devices using rodlike electrode arrangements have drawbacks. One is that the internal impedance may be excessively high. Another is that internal electrical short circuits may be present or may develop between electrodes of opposite polarity. This problem becomes more significant as the diameter of the electrodes is made smaller. The use of ever-smaller electrodes is a desirable goal because the available surface area per unit volume of the storage cell increases with decreasing electrode cylindrical diameter. Thus, in recent generations of electrical storage devices using rodlike electrodes the problem of internal electrical shorts has become of more concern. Finally, there is the ongoing desire to develop greater storage capacities in such devices, with lower manufacturing costs.
There is thus an ongoing need for improved electrical storage devices using rodlike electrodes, particularly where the electrode diameters are made quite small. The present invention fulfills this need, and further provides related advantages.